Image forming apparatuses such as color copiers and color printers are widely used, and color facsimile apparatuses are developed as image communication apparatuses.
Communication methods of the color facsimile apparatuses are standardized as the ITU-T Recommendations T.30, T.4, T.42 and T.81. For color image coding, the JPEG (Joint Photographic Experts Group) method in the Recommendation T.81 is adopted.
In the color facsimile apparatus standardized in the Recommendation T.30, as the necessary minimum color image data format, a main scanning width of A4 and a resolution of 200 dpi are defined; and as an option format, one of main scanning widths of B4 and A3, and one of resolutions of 100 dpi, 300 dpi and 400 dpi can be selected.
As color image printing methods, a sublimation thermal-transfer method, a thermal-wax method, an electrophotographic method, an ink-jet method and the like are known. Color reproducibility differs in accordance with printing method, and further, the color reproducibility differs in accordance with type of print sheet, or type or composition of ink.
On the other hand, an apparatus which does not have a color facsimile function as a single apparatus, but has the color facsimile function when connected to a device such as a personal computer (PC) where facsimile application software (hereinbelow referred to as “FAX software”) runs, has been developed. Even application software which supports only monochrome data can transmit a color image by this apparatus.
In a case where the above apparatus and the application software that supports only monochrome data are used for facsimile transmission, if a cover page is in color, a color image is transmitted. In this transmission, encoding time is longer and decoding time on the receiving side is longer in comparison with monochrome image transmission. Accordingly, users must bear waiting time longer than necessary. Further, in case of color image transmission, as the amount of data increases in comparison with monochrome image transmission, communication time increases and communication cost increases. Further, as the color image encoding is performed by using the JPEG method, a received image is degraded due to lossy data compression.
Even though the application software supports a color image, when there is a monochrome image and it is transmitted as a color image, a problem similar to the above problem occurs. Further, if a monochrome original image exists on the facsimile apparatus capable of color image transmission, a problem similar to the above problem occurs.
In other words, it is impossible to transmit an image of cover page, an image held by application software, and original image to be read, respectively in a mode desired by a user (monochrome, color and/or gray scale or the like) in one transmission process.